The thyroid/gonadal axis of the American alligator is being investigated. Two major areas of thyroid activity are examined, the poorly studied effect of thyroid hormones on the development of the ovary and testis and the 'permissive action' of thyroid hormones on sex steroid action. Specifically, the role (cooperative) the thyroid plays in the sexual differentiation of the gonads as well as its role in the development and functioning of the gonad during the neonatal and peripubertal periods is addressed. The developmental studies describe normal embryonic development of the thyroid and gonad with a focus on the presence, distribution and concentration of thyroid receptors (TRs), sex steroid receptors (ER- estrogen receptors, AR- androgen receptors), Dl (deiodinase gene) and ING2 [the Inhibition of Growth (ING) tumor suppressor gene 2]. Additionally, gonadal differentiation and development following exposure to an antithyroid-agent (PTU, proplythiouracil) during the window of sexual differentiation as well as during neonatal development is investigated. Quantitative RT-PCR will be used to address these questions. Basic knowledge on the role the thyroid plays in gonad development and function will aid in the prevention of related disorders. [unreadable] [unreadable]